"Geopolitics are often big drivers in oil markets," said Greg McKenna, chief market strategist at AxiTrader. "The U.S. strike against a regime that is backed by the Russians, and in a country where the Iranians are active as well supporting the regime has the potential to cause further political ructions."

The potential reactions from Iran and Russia, both major oil producers, "will keep oil traders on edge," he said. "That uncertainty supports prices ... in the very immediate term."

Syria itself is not a major oil producer, but the country is uncomfortably close to the Strait of Hormuz -- a critical chokepoint through which millions of barrels of oil are shipped each day.

Trump said the missile strike was in retaliation for a chemical weapons attack on civilians earlier this week that the U.S. says was carried out by the Syrian government.